This invention relates to a hard facing nickel-base alloy which is not only highly to wear, corrosion, errosion and heat but also particularly suitable for application to relatively small-sized pieces of base metal by gas welding.
It has been customary to apply a hard facing alloy to the surface of an object such as the disc or seat ring of a valve made of cast steel so as to prevent wear, corrosion, errosion, etc. of the material at high temperature.
Among various hard facing alloys there is known a cobalt-base alloy consisting of 26 to 29% by weight of chromium (Cr), 4 to 6% by weight of tungsten (W), 0.9 to 1.2% by weight of carbon (C), up to 1.5% by weight of silicon (Si) and up to 3% by weight of iron (Fe), the balance being cobalt (Co). The cobalt-base alloy has a hardness of 38 to 47 to Rockwell C scale and is superior in wear and corrosion resistance at high temperature. However, in recent years the price of cobalt has taken a jump due to shortage of resources so that the above-mentioned cobalt-base alloy has become very expensive. Therefore, there has been a constant demand for low-priced hard facing nickel-base alloys which can replace the cobalt-base alloy.
In an effort to meet the demand the present inventors have conducted various studies and experiments and already invented highly tough hard facing nickel-base alloys such that when they have been applied onto a large piece of base metal or a base of a metal having a thermal expansion coefficient greatly different from that of the alloy, no cracks or fissures occur in the applied alloy layer. The alloys have been disclosed in Japanese patent application Nos. 53-30709 and 53-103402 and PCT application No. PCT/JP 79/00026.
Indeed the above-mentioned alloys have good weldability onto the surface of the disc or seat ring of a large-sized valve made of cast steel, but they have a disadvantage that when applied onto the surface of a relatively small object, e.g., the disc or seat ring of a small-sized valve having a diameter of less than 25 mm, porosity is likely to be formed in the hard facing layer.
Gas welding and TIG welding can be used for application of hard facing alloy onto the surface of an article such as the disc or seat ring of a valve made of cast steel. Gas welding, however, is more commonly employed on a relatively small object such as the above-mentioned small-sized valve having a diameter of less than 25 mm. If TIG welding is employed, dilution of the hard facing layer with the base metal is high due to the small size of the base. This is undesirable.
When the previously mentioned cobalt-base alloy is used for hard facing of a small article such as mentioned above, porosity is unlikely to be formed in the hard facing layer. After extensive examination of the reasons why this is so the present inventors have found out that if a nickel-base alloy has (1) a solidus line have 1200.degree. C. and (2) a liquidus line below 1350.degree. C., porosity is seldom produced in the hard facing layer of the alloy formed on relatively small-sized articles such as mentioned above.
Based on the above findings, the present inventors have studied and examined various compositions of nickel-base alloys and accomplished the present invention.
One object of this invention is to provide a hard facing nickel-base alloy which satisfies the above two conditions and is superior in wear resistance and corrosion resistance at high temperature as well as other characteristics.
Other objects features and advantages of the invention will become apparent from the following detailed description with reference to the accompanying drawings.